linux.git/drivers/tty/hvc, branch v4.19

tty: hvc: hvc_write() fix break condition

2018-09-10T16:04:31+00:00

Commit 550ddadcc758 ("tty: hvc: hvc_write() may sleep") broke the
termination condition in case the driver stops accepting characters.
This can result in unnecessary polling of the busy driver.

Restore it by testing the hvc_push return code.

Tested-by: Matteo Croce 
Tested-by: Jason Gunthorpe 
Tested-by: Leon Romanovsky 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Greg Kroah-Hartman

tty: hvc: hvc_poll() fix read loop batching

2018-09-10T16:04:31+00:00

Commit ec97eaad1383 ("tty: hvc: hvc_poll() break hv read loop")
removes get_chars batching entirely, which slows down large console
operations like paste -- virtio console "feels worse than a 9600 baud
serial line," reports Matteo.

This adds back batching in a more latency friendly way. If the caller
can sleep then we try to fill the entire flip buffer, releasing the
lock and scheduling between each iteration. If it can not sleep, then
batches are limited to 128 bytes. Matteo confirms this fixes the
performance problem.

Latency testing the powerpc OPAL console with OpenBMC UART with a
large paste shows about 0.25ms latency, which seems reasonable. 10ms
latencies were typical for this case before the latency breaking work,
so we still see most of the benefit.

  kopald-1204    0d.h.    5us : hvc_poll <-hvc_handle_interrupt
  kopald-1204    0d.h.    5us : __hvc_poll <-hvc_handle_interrupt
  kopald-1204    0d.h.    5us : _raw_spin_lock_irqsave <-__hvc_poll
  kopald-1204    0d.h.    5us : tty_port_tty_get <-__hvc_poll
  kopald-1204    0d.h.    6us : _raw_spin_lock_irqsave <-tty_port_tty_get
  kopald-1204    0d.h.    6us : _raw_spin_unlock_irqrestore <-tty_port_tty_get
  kopald-1204    0d.h.    6us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.    7us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.    7us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.   36us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   36us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   36us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.   65us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   65us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   66us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.   94us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   95us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.   95us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  124us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  124us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  125us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  154us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  154us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  154us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  183us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  184us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  184us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  213us : tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  213us : __tty_buffer_request_room <-__hvc_poll
  kopald-1204    0d.h.  213us+: opal_get_chars <-__hvc_poll
  kopald-1204    0d.h.  242us : _raw_spin_unlock_irqrestore <-__hvc_poll
  kopald-1204    0d.h.  242us : tty_flip_buffer_push <-__hvc_poll
  kopald-1204    0d.h.  243us : queue_work_on <-tty_flip_buffer_push
  kopald-1204    0d.h.  243us : tty_kref_put <-__hvc_poll
  kopald-1204    0d.h.  243us : hvc_kick <-hvc_handle_interrupt
  kopald-1204    0d.h.  243us : wake_up_process <-hvc_kick
  kopald-1204    0d.h.  244us : try_to_wake_up <-hvc_kick
  kopald-1204    0d.h.  244us : _raw_spin_lock_irqsave <-try_to_wake_up
  kopald-1204    0d.h.  244us : _raw_spin_unlock_irqrestore <-try_to_wake_up

Reported-by: Matteo Croce 
Tested-by: Matteo Croce 
Tested-by: Jason Gunthorpe 
Tested-by: Leon Romanovsky 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Greg Kroah-Hartman

tty: hvc: hvc_poll() fix read loop hang

2018-09-10T16:04:31+00:00

Commit ec97eaad1383 ("tty: hvc: hvc_poll() break hv read loop") causes
the virtio console to hang at times (e.g., if you paste a bunch of
characters to it.

The reason is that get_chars must return 0 before we can be sure the
driver will kick or poll input again, but this change only scheduled a
poll if get_chars had returned a full count. Change this to poll on
any > 0 count.

Reported-by: Matteo Croce 
Reported-by: Jason Gunthorpe 
Tested-by: Matteo Croce 
Tested-by: Jason Gunthorpe 
Tested-by: Leon Romanovsky 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Greg Kroah-Hartman

powerpc/powernv: provide a console flush operation for opal hvc driver

2018-08-20T10:19:54+00:00

Provide the flush hv_op for the opal hvc driver. This will flush the
firmware console buffers without spinning with interrupts disabled.

Cc: Benjamin Herrenschmidt 
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

Merge branch 'topic/hvc' into next

2018-08-13T06:04:10+00:00

This branch held some hvc related commits (Hypervisor Virtual Console)
so that they could get some wider testing in linux-next before merging.

tty: hvc: remove unexplained "just in case" spin delay

2018-07-24T12:09:58+00:00

This delay was in the very first OPAL console commit 6.5 years ago,
and came from the vio hvc driver. The firmware console has hardened
sufficiently to remove it.

Reviewed-by: Benjamin Herrenschmidt 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powerpc/powernv: implement opal_put_chars_atomic

2018-07-24T12:09:57+00:00

The RAW console does not need writes to be atomic, so relax
opal_put_chars to be able to do partial writes, and implement an
_atomic variant which does not take a spinlock. This API is used
in xmon, so the less locking that is used, the better chance there
is that a crash can be debugged.

Cc: Benjamin Herrenschmidt 
Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

powerpc/powernv: move opal console flushing to udbg

2018-07-24T12:09:57+00:00

OPAL console writes do not have to synchronously flush firmware /
hardware buffers unless they are going through the udbg path.

Remove the unconditional flushing from opal_put_chars. Flush if
there was no space in the buffer as an optimisation (callers loop
waiting for success in that case). udbg flushing is moved to
udbg_opal_putc.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

tty: hvc: introduce the hv_ops.flush operation for hvc drivers

2018-07-23T10:13:20+00:00

Use .flush to wait for drivers to flush their console outside of
the spinlock, to reduce lock/irq latencies.

Flush the hvc console driver after each write, which can help
messages make it out to the console after a crash.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman

tty: hvc: hvc_write() may sleep

2018-07-23T10:12:32+00:00

Rework the hvc_write loop to drop and re-take the spinlock on each
iteration, add a cond_resched. Don't bother with an initial hvc_push
initially, which makes the logic simpler -- just do a hvc_push on
each time around the loop.

Signed-off-by: Nicholas Piggin 
Signed-off-by: Michael Ellerman